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<Head>
<Title>Boost Graph Library: predecessor_recorder</Title>
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<H1>
<pre>
predecessor_recorder&lt;PredecessorMap, EventTag&gt;
</pre>
</H1>

This is an <a href="./EventVisitor.html">EventVisitor</a> that records
the predecessor (or parent) of a vertex in a predecessor property
map. This is particularly useful in graph search algorithms where
recording the predecessors is an efficient way to encode the search
tree that was traversed during the search. The predecessor recorder is
typically used with the <tt>on_tree_edge</tt> or
<tt>on_relax_edge</tt> events and cannot be used with vertex events.

<p>
<tt>predecessor_recorder</tt> can be used with graph algorithms by
wrapping it with an algorithm-specific adaptor, such as <a
href="./bfs_visitor.html"><tt>bfs_visitor</tt></a> and <a
href="./dfs_visitor.html"><tt>dfs_visitor</tt></a>. Also, this event
visitor can be combined with other event visitors using
<tt>std::pair</tt> to form an EventVisitorList.

<p>
Algorithms such as Dijkstra's and breadth-first search will not assign
a predecessor to the source vertex (which is the root of the search
tree). It is often useful to initialize the source vertex's
predecessor to itself, thereby identifying the root vertex as the only
vertex which is its own parent. When using an algorithm like
depth-first search that creates a forest (multiple search trees) it
is useful to initialize the predecessor of every vertex to itself. This
way all the root nodes can be distinguished.


<h3>Example</h3>

See the example for <a href="./bfs_visitor.html"><tt>bfs_visitor</tt></a>.

<h3>Model of</h3>

<a href="./EventVisitor.html">EventVisitor</a>


<H3>Where Defined</H3>

<P>
<a href="../../../boost/graph/visitors.hpp">
<TT>boost/graph/visitors.hpp</TT></a>

<H3>Template Parameters</H3>

<P>
<TABLE border>
<TR>
<th>Parameter</th><th>Description</th><th>Default</th>
</tr>

<TR><TD><TT>PredecessorMap</TT></TD>
<TD>
A <a
href="../../property_map/doc/WritablePropertyMap.html">WritablePropertyMap</a>
where the key type and the value type are the vertex descriptor type
of the graph.
</TD>
<TD>&nbsp;</TD>
</TR>

<TR><TD><TT>EventTag</TT></TD>
<TD>
The tag to specify when the <tt>predecessor_recorder</tt> should be
applied during the graph algorithm. <tt>EventTag</tt> must be an
edge event.
</TD>
<TD>&nbsp;</TD>
</TR>

</table>

<H2>Associated Types</H2>

<table border>

<tr>
<th>Type</th><th>Description</th>
</tr>

<tr>
<td><tt>predecessor_recorder::event_filter</tt></td>
<td>
This will be the same type as the template parameter <tt>EventTag</tt>.
</td>
</tr>

</table>

<h3>Member Functions</h3>

<p>

<table border>
<tr>
<th>Member</th><th>Description</th>
</tr>

<tr>
<td><tt>
predecessor_recorder(PredecessorMap pa);
</tt></td>
<td>
Construct a predecessor recorder object with predecessor property map
<tt>pa</tt>.
</td>
</tr>

<tr>
<td><tt>
template &lt;class Edge, class Graph&gt;<br>
void operator()(Edge e, const Graph& g);
</tt></td>
<td>
Given edge <i>e = (u,v)</i>, this records <i>u</i> as the
predecessor (or parent) of <i>v</i>.
</td>
</tr>

</table>

<h3>Non-Member Functions</h3>

<table border>
<tr>
<th>Function</th><th>Description</th>
</tr>

<tr><td><tt>
template &lt;class PredecessorMap, class Tag&gt;<br>
predecessor_recorder&lt;PredecessorMap, Tag&gt; <br>
record_predecessors(PredecessorMap pa, Tag);
</tt></td><td>
A convenient way to create a <tt>predecessor_recorder</tt>.
</td></tr>

</table>

<h3>See Also</h3>

<a href="./visitor_concepts.html">Visitor concepts</a>
<p>
The following are other event visitors: <a
<a href="./distance_recorder.html"><tt>distance_recorder</tt></a>,
<a href="./time_stamper.html"><tt>time_stamper</tt></a>,
and <a href="./property_writer.html"><tt>property_writer</tt></a>.


<br>
<HR>
<TABLE>
<TR valign=top>
<TD nowrap>Copyright &copy; 2000-2001</TD><TD>
<A HREF="http://www.boost.org/people/jeremy_siek.htm">Jeremy Siek</A>,
Indiana University (<A
HREF="mailto:jsiek@osl.iu.edu">jsiek@osl.iu.edu</A>)<br>
<A HREF="http://www.boost.org/people/liequan_lee.htm">Lie-Quan Lee</A>, Indiana University (<A HREF="mailto:llee@cs.indiana.edu">llee@cs.indiana.edu</A>)<br>
<A HREF="https://homes.cs.washington.edu/~al75">Andrew Lumsdaine</A>,
Indiana University (<A
HREF="mailto:lums@osl.iu.edu">lums@osl.iu.edu</A>)
</TD></TR></TABLE>

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